Under-screen fingerprint identification device

ABSTRACT

An under-screen fingerprint identification device includes an image sensing element, a display element, an optical lens, and a band pass filter element. The band pass filter element is disposed between the image sensing element and the display element. An object to be identified reflects an initial beam to generate a sensing beam, and the sensing beam is transmitted to the image sensing element through the display element, the optical lens, and the band pass filter element. The band pass filter element allows a beam with a specific wavelength range to pass. The specific wavelength range and a wavelength range of the initial beam are partially overlapped.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of U.S. provisional application Ser. No. 62/712,990, filed on Aug. 1, 2018. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND Technical Field

The disclosure relates to an under-screen fingerprint identification device.

Description of Related Art

The rise of mobile payment brings about rapid expansion of the demand for biometric identification, and biometric identification technology can be divided into fingerprint identification technology, iris recognition technology, DNA identification technology, and so forth. In consideration of the need for efficiency, safety, and non-intrusion, fingerprint identification has gradually become the mainstream technology of biometric identification.

At present, among the fingerprint identification technologies, fingerprint on display (FOD) has been actively developed by various manufacturers. According to the FOD, physical buttons can be further removed, and a sensing element of the fingerprint identification is directly disposed below the display element, so as to achieve a higher screen-to-body ratio and comply with the requirements for the existing slim border display devices.

Compared to the conventional capacitive fingerprint identification, FOD allows the sensing beam to enter the sensing element through the display element and a plurality of optical film layers, and accordingly the intensity of the beam entering the sensing element becomes weak. Therefore, it is usually necessary to improve the imaging quality by means of signal amplification, so as to increase the success rate of fingerprint identification.

Due to the difference in the intensity of the beam received from a central region of the image sensing element and the intensity of the beam received from a peripheral region of the image sensing element, the region having larger intensity is overly saturated during the signal amplification process. As such, certain details of signals may be missing, which results in poor sensing quality.

SUMMARY

The disclosure provides an under-screen fingerprint identification device with good fingerprint identification performance.

According to an embodiment of the disclosure, an under-screen fingerprint identification device includes an image sensing element, a display element, an optical lens, and a band pass filter element. The image sensing element is disposed below the display element. The optical lens is disposed between the image sensing element and the display element. The band pass filter element is disposed between the image sensing element and the display element. An object to be identified is disposed on the display element. An initial beam is incident to the object to be identified, the object to be identified reflects the initial beam to generate a sensing beam, and the sensing beam is transmitted to the image sensing element through the display element, the optical lens, and the band pass filter element. The band pass filter element allows a beam with a specific wavelength range to pass. The specific wavelength range and a wavelength range of the initial beam are partially overlapped.

In an embodiment of the disclosure, the wavelength range of the initial beam is within a range from λ_(L1) to λ_(L2), the sensing beam includes a first sub-beam, an incidence angle θ1 between the first sub-beam and a normal line of the band pass filter element is substantially 0°, the band pass filter element has a first filter frequency spectrum corresponding to the first sub-beam, a transmittance rate corresponding to the first filter frequency spectrum at a wavelength λ_(F11) and a wavelength λ_(F12) is 50%, the wavelength λ_(F11) is shorter than the wavelength λ_(F12), and λ_(L1)≤λ_(F11)<λ_(L2).

In an embodiment of the disclosure, the band pass filter element is disposed between the image sensing element and the optical lens.

In an embodiment of the disclosure, the band pass filter element is disposed between the display element and the optical lens.

In an embodiment of the disclosure, the sensing beam further includes a second sub-beam, an incidence angle θ2 between the second sub-beam and the normal line of the band pass filter element is greater than the incidence angle θ1 between the first sub-beam and the normal line of the band pass filter element, the band pass filter element has a second filter frequency spectrum corresponding to the second sub-beam, a transmittance rate corresponding to the second filter frequency spectrum at a wavelength λ_(F21) and a wavelength λ_(F22) is 50%, the wavelength λ_(F21) is shorter than the wavelength λ_(F22), and λ_(F21)<λ_(F11).

In an embodiment of the disclosure, λ_(L1)≤λ_(F21)<λ_(F11).

In an embodiment of the disclosure, λ_(F21)<λ_(L1).

In an embodiment of the disclosure, a full width at half maximum (FWHM) of the first filter frequency spectrum is greater than an FWHM of the initial beam.

In an embodiment of the disclosure, the display element emits the initial beam.

According to an embodiment of the disclosure, an under-screen fingerprint identification device is configured to identify an object to be identified and includes an image sensing element, a display element, and an optical lens. The image sensing element is disposed below the display element. The optical lens is disposed between the image sensing element and the display element, wherein an initial beam generates a light spot on the display element, the light spot includes a central portion and a peripheral portion outside the central portion, and a brightness of the peripheral portion is greater than a brightness of the central portion.

In an embodiment of the disclosure, the initial beam includes a central sub-beam and a peripheral sub-beam, the central sub-beam defines the central portion of the light spot on the display element, the peripheral sub-beam defines the peripheral portion of the light spot on the display element, the central sub-beam passes through an optical axis region of the optical lens, and the peripheral sub-beam passes through a peripheral region of the optical lens.

In view of the above, the under-screen fingerprint identification device provided in one or more embodiments of the disclosure includes the band pass filter element. The band pass filter element has different filter spectrums corresponding to different beams with different incidence angles, and thus the brightness at the edge of the image sensing element can be compensated, and the identification quality of the under-screen fingerprint identification device can be compensated.

Besides, in the under-screen fingerprint identification device provided in another embodiment, the brightness distribution of the light spot generated by the initial beam is not uniform. Specifically, the light spot has a central portion with small brightness and a peripheral portion with large brightness, the initial beam includes a central sub-beam and a peripheral sub-beam, the central sub-beam defines the central portion of the light spot on the display element, the peripheral sub-beam defines the peripheral portion of the light spot on the display element, the central sub-beam passes through an optical axis region of the optical lens, and the peripheral sub-beam passes through a peripheral region of the optical lens. The intensity of the peripheral sub-beam is greater than the intensity of the central sub-beam, and therefore the peripheral sub-beam can compensate for lens shading, and the identification quality of the under-screen fingerprint identification device can be further improved.

To make the above features and advantages provided in one or more of the embodiments of the disclosure more comprehensible, several embodiments accompanied with drawings are described in detail as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the disclosure and, together with the description, serve to explain the principles described herein.

FIG. 1 is a schematic cross-sectional view of an under-screen fingerprint identification device according to an embodiment of the disclosure.

FIG. 2 illustrates that a band pass filter element of an under-screen fingerprint identification device has a first filter frequency spectrum S_(F1) corresponding to a first sub-beam L1, a second filter frequency spectrum S_(F2) corresponding to a second sub-beam L2, a third filter frequency spectrum S_(F3) corresponding to a third sub-beam L3, a fourth filter frequency spectrum S_(F4) corresponding to a fourth sub-beam L4, and a light emitting frequency spectrum S_(L) of an initial beam L according to an embodiment of the disclosure.

FIG. 3A is a schematic top view of an image sensing element according to an embodiment of the disclosure.

FIG. 3B illustrates a light distribution curve I on an image sensing element at the line segment A-A′ depicted in FIG. 3A and a light distribution curve Iref on an image sensing element of an under-screen fingerprint identification device according to a comparison example.

FIG. 4 is a schematic cross-sectional view of an under-screen fingerprint identification device according to another embodiment of the disclosure.

FIG. 5 is a schematic cross-sectional view of an under-screen fingerprint identification device according to still another embodiment of the disclosure.

FIG. 6A illustrates a light spot P on a display element 120.

FIG. 6B is a schematic view illustrating a brightness distribution of a central portion and a peripheral portion of a light spot P corresponding to the line segment B-B′ depicted in FIG. 6A.

FIG. 7 illustrates a light distribution curve S1 of the light spot P on the image capturing element 110 of the under-screen fingerprint identification device 100C after the light spot P on the display element 120 of the under-screen fingerprint identification device 100C depicted in FIG. 5 is reflected by an object 10 to be identified.

FIG. 8 illustrates a light spot P′ on a display element of an under-screen fingerprint identification device according to a comparison example.

FIG. 9 illustrates a light distribution curve S1′ of the light spot P′ on an image capturing element of an under-screen fingerprint identification device after the light spot P′ on a display element of the under-screen fingerprint identification device in a comparison example is reflected by an object to be identified.

DESCRIPTION OF THE EMBODIMENTS

In the disclosure and in the following claims, various terms will be described and defined as having the following definitions: “optional” or “optionally” means that the subsequently stated situation may or may not occur. Hence, the description includes the occurrence or non-occurrence of the situation. For instance, if a device optionally includes a characteristic element for a sample collection unit, it indicates that the sample collection unit may or may not be present, and as such, the description includes that one of the devices has or does not have the structure of the sample collection unit.

As used herein, “substantial” means more than the minimum or ineffective amount, and “substantially” means more than the minimum or ineffectively. For instance, if the term “substantially different” is used herein, it means that there is a sufficient degree of difference between two values, so that people skill in the art will consider the difference between the two values within the context of the characteristics measured by the equivalent value, which is statistically significant. Thus, the difference between the two values that are substantially different from each other is typically greater than about 10%, and can be greater than about 20%, greater than about 30%, greater than about 40%, or greater than about 50%, which may vary together with a reference value or a function of a comparison value.

FIG. 1 is a schematic cross-sectional view of an under-screen fingerprint identification device according to an embodiment of the disclosure. FIG. 2 illustrates that a band pass filter element of an under-screen fingerprint identification device has a first filter frequency spectrum S_(F1) corresponding to a first sub-beam L1, a second filter frequency spectrum S_(F2) corresponding to a second sub-beam L2, a third filter frequency spectrum S_(F3) corresponding to a third sub-beam L3, a fourth filter frequency spectrum S_(F4) corresponding to a fourth sub-beam L4, and a light emitting frequency spectrum S_(L) of an initial beam L according to an embodiment of the disclosure. The first sub-beam L1, the second sub-beam L2, the third sub-beam L3, and the fourth sub-beam L4 are respectively incident to the band pass filter element 140 at an incidence angle θ1, an incidence angle θ2, an incidence angle θ3, and an incidence angle θ4. The incidence angle θ1, the incidence angle θ2, the incidence angle θ3, and the incidence angle θ4 may be but are not limited to 0°, 10°, 20°, and 30°, respectively.

With reference to FIG. 1 and FIG. 2, in an embodiment of the disclosure, an under-screen fingerprint identification device 100A includes an image sensing element 110, a display element 120, an optical lens 130, and a band pass filter element 140. The image sensing element 110 is disposed below the display element 120. The optical lens 130 is disposed between the image sensing element 110 and the display element 120. The band pass filter element 140 is disposed between the image sensing element 110 and the display element 120. For instance, in the present embodiment, the band pass filter element 140 can be optically disposed between the image sensing element 110 and the optical lens 130, which should however not be construed as a limitation in the disclosure. In the present embodiment, the image sensing element 110 can include a plurality of sensing regions (not shown) arranged on a plane in an X direction and a Y direction, and the image sensing element 110, the display element 120, the optical lens 130, and the band pass filter element 140 can be arranged along a Z direction perpendicular to the X direction and the Y direction.

In the present embodiment, the image sensing element 110 can be a complementary metal oxide semiconductor image sensor (CMOS image sensor, CIS), a charge coupled device (CCD), or any other appropriate type of image sensing element.

In the present embodiment, the display element 120 can be a self-illuminating display element including but not limited to an organic light-emitting diode (OLED). This should however not be construed as a limitation in the disclosure; according to other embodiments, the display element 120 may also be a non-self-illuminating display element including but not limited to a liquid crystal display (LCD) element.

According to the present embodiment, the optical lens 130 can be a lens assembly having a plurality of lenses. For instance, the lenses can be a bi-convex lens, a bi-concave lens, a plano-convex lens, a plano-concave lens, a convex-concave lens, any other lens, or a combination of at least two of the aforesaid lenses. A sensing beam L′ reflected by an object 10 forms images onto the image sensing element 110 by the optical lens 130.

In the present embodiment, the under-screen fingerprint identification device 100A can further include a casing 150 configured to accommodate the optical lens 130. The casing 150 can optically accommodate the band pass filter element 140 and the image sensing element 110, which should however not be construed as a limitation in the disclosure. Besides, the under-screen fingerprint identification device 100A can optically include a substrate 160 and a translucent cover 170. The substrate 160 can be configured to hold the image sensing element 110. The translucent cover 170 is disposed on the display element 120 to protect the display element 120. The translucent cover 170 has an upper surface 170 s where the object 10 to be identified is adapted to be disposed. That is, the upper surface 170 s of the translucent cover 170 may be a surface of the under-screen fingerprint identification device 100A receiving a pressing action, which should however not be construed as a limitation in the disclosure.

In the present embodiment, the under-screen fingerprint identification device 100A can further include an amplifier (not shown) electrically connected to the image sensing element 110. The image sensing element 110 is configured to receive a sensing beam L′ and convert the same to a corresponding electric signal, and the amplifier is configured to amplify the electric signal output by the image sensing element 110.

With reference to FIG. 1, in the present embodiment, the object 10 to be identified is disposed on the display element 120, the initial beam L is incident to the object 10 to be identified, and the object 10 to be identified reflects the initial beam L to generate the sensing beam L′. The sensing beam L′ is transmitted to the image sensing element 110 through the display element 120, the optical lens 130, and the band pass filter element 140. In the present embodiment, the display element 120 is, for instance, a self-illuminating display element, and the initial beam L can be emitted from the display element 120. This should however not be construed as a limitation in the disclosure; in other embodiments, the initial beam L may also be emitted from another light source. In the present embodiment, the object 10 to be identified may be fingerprints, vein, or any other biological features, which should however not be construed as a limitation in the disclosure.

Particularly, after the initial beam L is reflected by the object 10 to be identified, the sensing beam L′ having the information of the object 10 to be identified (e.g., ridges and valleys of fingerprints) is generated. The sensing beam L′ can include a first sub-beam L1, a second sub-beam L2, a third sub-beam L3, and a fourth sub-beam L4, wherein incidence angles θ1, θ2, θ3, and θ4 are respectively formed between the a normal line N of the band pass filter element 140 and the first sub-beam L1, the second sub-beam L2, the third sub-beam L3, and the fourth sub-beam L4, respectively. The incidence angle θ1 is substantially 0°, and θ1<θ2<θ3<θ4<90°. However, this should not be construed as a limitation in the disclosure. In other embodiments, the sensing beam L′ may include more sub-beams, and different incidence angles can be formed between the normal line N of the band pass filter element 140 and the sub-beams. In the present embodiment, the first sub-beam L1, the second sub-beam L2, the third sub-beam L3, and the fourth sub-beam L4 are exemplary and does not indicate that the sensing beam L′ provided herein merely has four sub-beams.

With reference to FIG. 1 and FIG. 2, in the present embodiment, a wavelength range of the light emitting frequency spectrum S_(L) of the initial beam L is within a range from λ_(L1) to λ_(L2), and the wavelength λ_(L1) is shorter than the wavelength λ_(L2) For instance, in the present embodiment, λ_(L1) can be 400 nm, and λ_(L2) can be 700 nm; preferably, λ_(L1) can be 380 nm, and λ_(L2) can be 630 nm. That is, the wavelength range of the light emitting frequency spectrum S_(L) of the initial beam L is about the wavelength range of a green beam, which should however not be construed as a limitation in the disclosure.

In the present embodiment, the band pass filter element 140 has the first filter frequency spectrum S_(F1), the second filter frequency spectrum S_(F2), the third filter frequency spectrum S_(F3), and the fourth filter frequency spectrum S_(F4) respectively corresponding to the first sub-beam L1, the second sub-beam L2, the third sub-beam L3, and the fourth sub-beam L4. A transmittance rate corresponding to the first filter frequency spectrum S_(F1) at a wavelength λ_(F11) and a wavelength λ_(F12) is 50%, the wavelength λ_(F21) is shorter than the wavelength λ_(F22), and λ_(L1)≤λ_(F11)<λ_(L2). A transmittance rate corresponding to the second filter frequency spectrum S_(F2) at a wavelength λ_(F21) and a wavelength λ_(F22) is 50%, the wavelength λ_(F21) is shorter than the wavelength λ_(F22), and λ_(F21)<λ_(F11); preferably, λ_(L1)≤λ_(F21)<λ_(F11). A transmittance rate corresponding to the third filter frequency spectrum S_(F3) at a wavelength λ_(F31) and a wavelength λ_(F32) is 50%, the wavelength λ_(F31) is shorter than the wavelength λ_(F32), and λ_(F31)<λ_(F21); preferably, λ_(L1)≤λ_(F31)<λ_(F21). A transmittance rate corresponding to the fourth filter frequency spectrum S_(F4) at a wavelength λ_(F41) and a wavelength λ_(F42) is 50%, the wavelength λ_(F41) is shorter than the wavelength λ_(F42), and λ_(F41)<λ_(F31); preferably, λ_(L1)≤λ_(F41)<λ_(F31). In the present embodiment, a full width at half maximum (FWHM) W_(F1) of the first filter frequency spectrum S_(F1) corresponding to the first sub-beam L1 is greater than the FWHM W_(L) of the light emitting frequency spectrum S_(L) of the initial beam L, a FWHM W_(F2) of the second filter frequency spectrum S_(F2) corresponding to the second sub-beam L2 may be greater than the FWHM W_(L) of the light emitting frequency spectrum S_(L) of the initial beam L, a FWHM W_(F3) of the filter frequency spectrum S_(F3) corresponding to the third sub-beam L3 may be greater than the FWHM W_(L) of the light emitting frequency spectrum S_(L) of the initial beam L, and a FWHM W_(F4) of the fourth filter frequency spectrum S_(F4) corresponding to the fourth sub-beam L4 may be greater than the FWHM W_(L) of the light emitting frequency spectrum S_(L) of the initial beam L. The FWHM refers to the difference between two wavelengths whose spectrum corresponds to the transmittance rate as 50%. For instance, the FWHM W_(F1) of the first filter frequency spectrum S_(F1) is λ_(F12)−λ_(F11), the FWHM W_(F2) of the second filter frequency spectrum S_(F2) is λ_(F22)−λ_(F21), the FWHM W_(F3) of the third filter frequency spectrum S_(F3) is λ_(F32)−λ_(F31), the FWHM W_(F4) of the fourth filter frequency spectrum S_(F4) is λ_(F42)−λ_(F41), and the FWHM W_(L) of the light emitting frequency spectrum S_(L) of the initial beam L is λ_(L4)−λ_(L3).

FIG. 3A is a schematic top view of an image sensing element according to an embodiment of the disclosure. FIG. 3B illustrates a light distribution (represented by a curve I) on an image sensing element at the line segment A-A′ depicted in FIG. 3A. FIG. 3B also illustrates a light distribution (represented by a curve Iref) on an image sensing element of an under-screen fingerprint identification device according to a comparison example. The difference between the under-screen fingerprint identification device in the comparison example and the under-screen fingerprint identification device 100A depicted in FIG. 1 lies in that the under-screen fingerprint identification device provided in the comparison example is not equipped with the band pass filter element 140. Besides, the x axis shown in FIG. 3B represents a distance to a center 110 c of the image sensing element 110, and the y axis shown in FIG. 3B represents a normalized brightness.

With reference to FIG. 1 to FIG. 3B, in the present embodiment, the sensing beam L′ is transmitted to the image sensing element 110 through the band pass filter element 140, thus resulting in corresponding brightness distribution in different regions on the image sensing element 110. In particular, when the first sub-beam L1, the second sub-beam L2, the third sub-beam L3, and the fourth sub-beam L4 of the sensing beam L′ are transmitted to the image sensing element 110, the first sub-beam L1 is transmitted to be close to the center 110 c of the image sensing element 110, and the second sub-beam L2, the third sub-beam L3, and the fourth sub-beam L4 are sequentially away from the center 110 c of the image sensing element 110.

With reference to FIG. 1 to FIG. 3B, the filter frequency spectrum of the band pass filter element 140 tends to be changed together with the incidence angle of the incident beam. Particularly, if the incidence angle increases from 0, the filter frequency spectrum of the band pass filter element 140 moves toward a short wave direction. That is, the second filter frequency spectrum S_(F2) corresponding to the second sub-beam L2 is, in comparison with the first filter frequency spectrum S_(F1) corresponding to the first sub-beam L1, closer to the short wave direction, the third filter frequency spectrum S_(F3) corresponding to the third sub-beam L3 is, in comparison with the second filter frequency spectrum S_(F2) corresponding to the second sub-beam L2, closer to the short wave direction, and the fourth filter frequency spectrum S_(F4) corresponding to the fourth sub-beam L4 is, in comparison with the third filter frequency spectrum S_(F3) corresponding to the third sub-beam L3, closer to the short wave direction.

Since the filter frequency spectrum of the band pass filter element 140 tends to be changed together with the incidence angle of the incident beam, the sub-beam with larger incidence angle is more likely to arrive at the image capturing element 110 through the band pass filter element 140 (i.e., when an incidence angle between the sub-beam and a normal line of the band pass filter element 140 is larger, the ratio of the amount of the sub-beam passing the band pass filter element 140 to the amount of the sub-beam not yet entering the band pass filter element 140 is higher). Specifically, the possibility of the fourth sub-beam L4 arriving at the image capturing element 110 through the band pass filter element 140 is greater than the possibility of the third sub-beam L3 arriving at the image capturing element 110 through the band pass filter element 140, the possibility of the third sub-beam L3 arriving at the image capturing element 110 through the band pass filter element 140 is greater than the possibility of the second sub-beam L2 arriving at the image capturing element 110 through the band pass filter element 140, and the possibility of the second sub-beam L2 arriving at the image capturing element 110 through the band pass filter element 140 is greater than the possibility of the first sub-beam L1 arriving at the image capturing element 110 through the band pass filter element 140. As such, the light distribution curve I on the image capturing element 110 of the under-screen fingerprint identification device 100A provided in the present embodiment is smoother than the light distribution curve Iref on the image capturing element of the under-screen fingerprint identification device provided in the comparison example, and the electric signal corresponding to the light distribution curve I is more suitable for being amplified by the amplifier, so as to better prevent the issue of over-saturation and the resultant loss of image details, which is conducive to the improvement of the identification quality of the under-screen fingerprint identification device 100A.

FIG. 4 is a schematic cross-sectional view of an under-screen fingerprint identification device according to another embodiment of the disclosure. The under-screen fingerprint identification device 100B depicted in FIG. 4 is similar to the under-screen fingerprint identification device 100A depicted in FIG. 1, while the difference therebetween lies in that the band pass filter element 140 is disposed between the display element 120 and the optical lens 130 according to the present embodiment. The other elements therein are arranged in a similar manner as the arrangement of the elements in the under-screen fingerprint identification device 100A depicted in FIG. 1, and the technical effects achieved by these elements are similar as well; hence, no further explanation will be provided hereinafter.

FIG. 5 is a schematic cross-sectional view of an under-screen fingerprint identification device according to still another embodiment of the disclosure. FIG. 6A illustrates a light spot P on a display element 120. FIG. 6B is a schematic view illustrating a brightness distribution of a central portion and a peripheral portion of a light spot P corresponding to the line segment B-B′ depicted in FIG. 6A. FIG. 7 illustrates a light distribution curve S1 of the light spot P on the image capturing element 110 of the under-screen fingerprint identification device 100C after the light spot P on the display element 120 of the under-screen fingerprint identification device 100C depicted in FIG. 5 is reflected by an object 10 to be identified.

With reference to FIG. 5, the under-screen fingerprint identification device 100C provided in the present embodiment is similar to the under-screen fingerprint identification device 100A depicted in FIG. 1, while the difference therebetween lies in that the under-screen fingerprint identification device 100C is not equipped with the band pass filter element, while the other optical elements therein are arranged in a similar manner as the arrangement of the optical elements in the under-screen fingerprint identification device 100A depicted in FIG. 1 and thus will not be further explained. Here, only the difference is addressed.

With reference to FIG. 5 to FIG. 6B, in the present embodiment, the under-screen fingerprint identification device 100C is configured to identify the object 10 to be identified and includes the image sensing element 110, the display element 120, and the optical lens 130. The display element 120 is disposed on the image sensing element 110. The optical lens 130 is disposed between the image sensing element 110 and the display element 120. The initial beam L generates a light spot P on the display element 120, the light spot P includes a central portion Pc and a peripheral portion Pe outside the central portion Pc, and a brightness of the peripheral portion Pe is greater than a brightness of the central portion Pc. In the present embodiment, the initial beam L includes a central sub-beam Lc and a peripheral sub-beam Le, the central sub-beam Lc defines the central portion Pc of the light spot P on the display element 120, the peripheral sub-beam Le defines the peripheral portion Pe of the light spot P on the display element 120, the central sub-beam Lc passes through an optical axis region 130 c of the optical lens 130, and the peripheral sub-beam Le passes through a peripheral region 130 e of the optical lens 130.

With reference to FIG. 6A and FIG. 6B, in the present embodiment, a brightness of the central portion Pc of the light spot P is Bc, a brightness of the peripheral portion Pe of the light spot P is Be, and Be>Bc. In the present embodiment, the light spot P has two brightnesses, i.e., the brightness Bc and the brightness Be. However, this should not be construed as a limitation in the disclosure. In other embodiments, a brightness at an intersection between the central portion Pc and the peripheral portion Pe can be gradually increased in a direction from the central portion Pc to the peripheral portion Pe.

FIG. 8 illustrates a light spot P′ on a display element of an under-screen fingerprint identification device according to a comparison example. FIG. 9 illustrates a light distribution curve S1′ of the light spot P′ on an image capturing element of an under-screen fingerprint identification device after the light spot P′ on a display element of the under-screen fingerprint identification device in a comparison example is reflected by an object to be identified. The difference between the under-screen fingerprint identification device provided in the comparison example and the under-screen fingerprint identification device 100C provided in the present embodiment lies in that the light intensity distribution of the light spot P′ on the display element of the under-screen fingerprint identification device in the comparison example is uniform. With reference to FIG. 8 and FIG. 9, after the light spot P′ on the display element of the under-screen fingerprint identification device provided in the comparison example is reflected by the object to be identified, due to the lens shading effects of the optical lens, an intensity difference ΔS1′ of the light distribution curve S1′ of the reflected light spot P′ on the image capturing element is significant. With reference to FIG. 6A, FIG. 6B, and FIG. 7, the light intensity distribution of the light spot P on the display element 120 of the under-screen fingerprint identification device 100C provided in the present embodiment is not uniform, and the light spot P′ with the non-uniform light intensity distribution and the lens shading effect of the optical lens 130 can compensate for each other, so as to reduce the height difference ΔS1 of the resultant light distribution curve S1 on the image capturing element 110. Thereby, the electric signal corresponding to the light distribution curve S1 is more suitable for being amplified by the amplifier, so as to better prevent the issue of over-saturation and the resultant loss of image details, which is conducive to the improvement of the identification quality of the under-screen fingerprint identification device 100C.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure provided in the disclosure without departing from the scope or spirit indicated herein. In view of the foregoing, it is intended that the disclosure cover modifications and variations provided they fall within the scope of the following claims and their equivalents. 

What is claimed is:
 1. An under-screen fingerprint identification device comprising: a display element; an image sensing element disposed below the display element; an optical lens disposed between the image sensing element and the display element; and a band pass filter element disposed between the image sensing element and the display element, wherein an object to be identified is disposed on the display element, an initial beam is incident to the object to be identified, the object to be identified reflects the initial beam to generate a sensing beam, and the sensing beam is transmitted to the image sensing element through the display element, the optical lens, and the band pass filter element; the band pass filter element allowing a beam with a specific wavelength range to pass, the specific wavelength range and a wavelength range of the initial beam being partially overlapped.
 2. The under-screen fingerprint identification device according to claim 1, wherein the wavelength range of the initial beam is within a range from λ_(L1) to λ_(L2), the sensing beam comprises a first sub-beam, an incidence angle θ1 between the first sub-beam and a normal line of the band pass filter element is substantially 0°, the band pass filter element has a first filter frequency spectrum corresponding to the first sub-beam, a transmittance rate corresponding to the first filter frequency spectrum at a wavelength λ_(F11) and a wavelength λ_(F12) is 50%, the wavelength λ_(F11) is shorter than the wavelength λ_(F12), and λ_(L1)≤λ_(F11)<λ_(L2).
 3. The under-screen fingerprint identification device according to claim 1, wherein the band pass filter element is disposed between the image sensing element and the optical lens.
 4. The under-screen fingerprint identification device according to claim 1, wherein the band pass filter element is disposed between the display element and the optical lens.
 5. The under-screen fingerprint identification device according to claim 2, wherein the sensing beam further comprises a second sub-beam, an incidence angle θ2 between the second sub-beam and the normal line of the band pass filter element is greater than the incidence angle θ1 between the first sub-beam and the normal line of the band pass filter element, the band pass filter element has a second filter frequency spectrum corresponding to the second sub-beam, a transmittance rate corresponding to the second filter frequency spectrum at a wavelength λ_(F21) and a wavelength λ_(F22) is 50%, the wavelength λ_(F21) is shorter than the wavelength λ_(F22), and λ_(F21)<λ_(F11).
 6. The under-screen fingerprint identification device according to claim 5, wherein λ_(L4)≤λ_(F21)<λ_(F11).
 7. The under-screen fingerprint identification device according to claim 5, wherein λ_(F21)<λ_(L1).
 8. The under-screen fingerprint identification device according to claim 1, wherein a full width at half maximum of the first filter frequency spectrum is greater than a full width at half maximum of the initial beam.
 9. The under-screen fingerprint identification device according to claim 1, wherein the display element emits the initial beam.
 10. An under-screen fingerprint identification device configured to identify an object to be identified and comprising: a display element; an image sensing element disposed below the display element; an optical lens disposed between the image sensing element and the display element, wherein an initial beam generates a light spot on the display element, the light spot comprises a central portion and a peripheral portion outside the central portion, and a brightness of the peripheral portion is greater than a brightness of the central portion.
 11. The under-screen fingerprint identification device according to claim 10, wherein the initial beam comprises a central sub-beam and a peripheral sub-beam, the central sub-beam defines the central portion of the light spot on the display element, the peripheral sub-beam defines the peripheral portion of the light spot on the display element, the central sub-beam passes through an optical axis region of the optical lens, and the peripheral sub-beam passes through a peripheral region of the optical lens. 